1. Field of the Invention
This invention is in the field of cyclic char fuel oxidation reactor plants wherein several char fuel masses within several separate primary reactors are first compressed with reactant air from a separate compressor followed by expansion of resulting reacted gas into a separate expander and this cycle of compression followed by expansion is repeated.
2. Description of the Prior Art
The following U.S. Patents describe several example types of cyclic char fuel oxidation reactor plants with which the improvements of this invention can be used:
U.S. Pat. No. 4,455,837; J. C. Firey, Jun. 26, 1984 PA1 U.S. Pat. No. 4,484,531; J. C. Firey, Nov. 27, 1984 PA1 U.S. Pat. No. 4,509,957; J. C. Firey, Apr. 9, 1985 PA1 U.S. Pat. No. 4,568,361; J. C. Firey, Feb. 4, 1986 PA1 U.S. Pat. No. 4,707,991; J. C. Firey, Nov. 24, 1987
In all of these example cyclic char fuel oxidation reactor plants the gaseous reactants, such as air, are compressed into the pore spaces of the char fuel contained within several primary reactors inside pressure vessel containers. Primary reaction of the gaseous reactants with the char fuel occurs within the pore spaces during compression. Expansion of these primary product gases then occurs out of the pore spaces of the char fuel. In some forms of cyclic char fuel oxidation reactor plant the primary product gases are further reacted with additional reactant gases in a secondary reaction within a secondary reaction chamber during expansion. This cycle of gas compression followed by expansion is repeated for each of the pressure vessel containers, with fresh gaseous reactants being supplied for each compression and with final product reacted gases being removed during each expansion. The descriptions of cyclic char fuel oxidation reactor plants contained in the above listed U.S. patents are incorporated herein by reference thereto. The compressors of these plants are separate from the expanders thereof, but may be driven thereby, as for example where a centrifugal compressor is driven via its input shaft by the output shaft of a gas turbine engine expander.
Several char fuel containers are used on these cyclic char fuel oxidation reactor plants and these are pressure vessel containers whose number at least equals the sum of the number of compressor stages plus the number of expander stages. Each of these containers is fitted with a refuel means for adding char fuel into the refuel end of the primary reactor and an ash removal means for removing ashes or spent char fuel material from the ash removal end of the primary reactor.
The compressor means of these cyclic char fuel reaction plants comprise one or more stages, as defined in the material incorporated by reference, and each such stage has a delivery end outlet at its high pressure end through which the compressed gas may flow out of a stage and into a connected char fuel container. The expander means of these cyclic char fuel reaction plants may be a work producing engine and comprise one or more stages, as defined in the material incorporated by reference, and each such stage has an inlet at its high pressure end through which the reacted gas may flow into the expander stage from the connected char fuel container. The expander can be a simple blow down expander of low cost. But in many cyclic char fuel oxidation reactor plants we will prefer to use an expander engine, such as a gas turbine in order to recover the available work of expansion. This expander engine work can be used to drive the compressor and to generate output work via a means for absorbing expander work such as an electric generator.
Each container has separate changeable gas flow connections to each delivery end outlet of each compressor stage and to each inlet each expander stage and these changeable gas flow connections comprise means for opening and closing these connections while the plant is operating. These several means for opening and closing are controlled by a means for controlling the opening and closing of the changeable gas flow connections so that:
1. Each container is opened for a time period to each outlet of each stage of the compressor, in a sub sequence of time periods of open gas flow connections to compressor stage outlets, proceeding in time order of increasing compressor stage delivery pressure.
2. Each container is opened for a time period to each inlet of each stage of the expander, in a sub sequence of time periods of open gas flow connections to expander stage inlets, proceeding in time order of decreasing expander stage inlet pressure.
3. A sub sequence of gas flow connections to expander stage inlets follows after each sub sequence of gas flow connections to compressor stage outlets, and these sub sequences are repeated.
4. During any one time period of these sub sequences of connections each container is open gas flow connected to but one stage of either the compressor or the expander.
5. During any one time period of these sub sequences of connections each stage is open gas flow connected to but one container.
Additional detailed descriptions of char fuel containers and changeable gas flow connections are presented in the material incorporated by reference, for example in U.S. Pat. No. 4,509,957, col. 14, line 46 through line 58, and col. 18, line 39 through line 52.
As used herein and in the claims the term char fuel is as defined in U.S. Pat. No. 4,509,957, col. 2, line 58 through 68, and in U.S. Pat. No. 4,455,837, col. 4, line 8 through line 16, and this material is incorporated herein by reference.
As used herein and in the claims the terms oxygen gas, and a gas containing appreciable oxygen gas, are as defined in U.S. Pat. No. 4,509,957, col. 3, line 1 through line 8 and in U.S. Pat. No. 4,455,837, col. 4, line 1 through line 7, and this material is incorporated herein by reference.
A means for preheating the char fuel within the primary reaction chamber is used to bring the char fuel up to that temperature at which it will react rapidly with oxygen in adjacent compressed gases while the plant is being started. Thereafter the means for preheating the char fuel can be turned off when the heat of the primary reaction becomes sufficient to keep the char fuel at or above this rapid reaction temperature. During starting a cranking means is used to drive the compressor.
As char fuel is reacted to ashes within the primary reactor it is replaced by a refuel mechanism means for supplying fresh char fuel into a refuel end of the primary reactor. The char fuel is thus moved along through the primary reactor toward an opposite ash collection end of the primary reactor. Hence the char fuel being reacted within the primary reactor has a direction of motion from the refuel end toward the ash collection end. An ash removal mechanism is used as a means for removing ashes from the primary reaction chamber.
Where air is the reactant gas it is readily available from the atmosphere. In some applications oxygen enriched air or essentially pure oxygen may be used as the reactant gas, as for example in some gasifier uses, and here a source of oxygen rich gas is needed.
The term producer gas is used herein and in the claims to mean those reacted gases emerging from the primary reactor during expansion and this is normally a fuel gas containing carbon monoxide and other components.
The term secondary reacted gas is used herein and in the claims to means those reacted gases within the secondary reactor, and for engines these are normally essentially complete combustion products containing carbon dioxide and other components.
For cyclic char fuel oxidation gasifiers the secondary reacted gas is normally also a producer gas since a secondary reaction is not used when char fuel gasification is the purpose.
The term fixed open gas flow connection is used herein and in the claims to mean a gas flow passage which remains open whenever the cyclic char fuel oxidation reactor is operating.
The term changeable gas flow connection is used herein and in the claims to mean a gas flow passage which can be opened or closed while the cyclic char fuel oxidation reactor plant is operating. A changeable gas flow connection is opened and closed by a means for opening and closing.
As the char fuel within the primary reactor moves along the char fuel motion direction, it is preheated by heat transfer from char fuel portions which are further along and are reacting rapidly with oxygen and thus are at a high temperature. Where the char fuel being used is essentially free of volatile matter, as with coke fuel, this preheat zone serves to bring the new char fuel up to its rapid reaction temperature. The char fuel then enters the rapid reaction zone and carbon reacts therein with oxygen to form producer gas. Beyond the rapid reaction zone in the direction of char fuel motion the char fuel is essentially completely reacted to ashes which pass into an ash collection zone at the end of the char fuel motion path.
When the char fuel being used contains volatile matter, as with bituminous coal, the preheat zone also serves to remove the volatile matter from the coal, in part by distillation and in part by reaction to volatile products. In the absence of oxygen, appreciable portions of this distilled volatile matter become tars and other portions become fuel gases of essentially hydrocarbon type. These tars from coal volatile matter are undesirable in a cyclic char fuel oxidation reactor as they tend to clog up the mechanical components of the expander and to foul any spark igniters used in the secondary reactor. Tars which are exhausted from the cyclic char fuel oxidation reactor plant are also an undesirable air pollutant material.
In prior art, steady pressure, gas producers tar formation from coal volatile matter has been successfully reduced by passing the primary reactant air first into the preheat and volatile matter distillation zone. The emerging volatile matter apparently reacts with oxygen in the air to form oxygenated hydrocarbon type materials which form much less tar. The resulting volatile matter-in-air mixture then passes into the rapid reaction zone. Within the rapid reaction zone the volatile matter-in-air mixture is apparently burned in appreciable part to fully reacted carbon dioxide and steam. The carbon dioxide and steam, plus any unreacted oxygen, then react with carbon in the rapid reaction zone to form producer gas which emerges from the primary reactor. One disadvantage of this method for reducing tar formation is that the initial burning of the volatile matter in air mixture on entering the rapid reaction zone creates very high temperatures there and ash fusion and clinkering may result. These clinkers clog up the motion of the char fuel along the char fuel motion direction and may encase carbon particles and thus prevent complete carbon gasification. Another disadvantage of this method for reducing tar formation is that the carbon dioxide and steam created by burnup of the volatile matter-in-air mixture, react much more slowly with hot carbon in the rapid reaction zone to form producer gas. In prior art, steady pressure, gas producers this latter disadvantage was overcome by use of deeper rapid reaction zones of larger cross sectional area so that the required producer gas reaction could be completed. But when primary producer gas reactors are to be used on cyclic char fuel oxidation reactor plants such large volume reactors are undesirable since very thick walls are needed on the pressure vessel containers. It would be very desirable to have available a method for reducing tar formation from high volatile matter char fuels which did not produce clinkers and did not require a large volume primary reactor.
In prior art cyclic char fuel oxidation reactors the ashes are removed from the ash collection zone of the primary reactor at the end of the char fuel motion path by an ash removal mechanism. Most such ash removal mechanisms remove a volume of material at intervals and it is necessary to control either the volume, or the interval, or both, so that only ashes, and no unburned char fuel, are removed. While such control means are feasible they are necessarily complex since it is difficult to sense the ash quantity and ash level existing within the ash collection zone. It would be desirable to have available an ash removal means which did not require such sensing of ash level within the primary reactor.